Styrenic resins which are used for exterior materials of electronic devices can also be used in a variety of engineering applications because of their excellent impact resistance, dimensional stability and high heat resistance. However, styrenic resins can burn easily and do not have fire resistance. Accordingly countries such as the United States, Japan and many European countries have passed laws requiring polymer resins to satisfy flame resistance standards.
A widely used and known method for imparting good flame retardancy to styrenic resin includes adding a halogen-containing compound as a flame retardant to a rubber-modified styrenic resin and adding an antimony-containing compound as a flame retardant aid. Examples of halogen-containing compounds used to impart flame retardancy include polybromodiphenyl ether, tetrabromobisphenol-A, epoxy compounds substituted with bromine, chlorinated polyethylene, and the like. Antimony trioxide or antimony pentaoxide is commonly used as an antimony-containing compound.
When a halogen- and antimony-containing compound is used to improve flame retardancy of resins, a desired degree of flame retardancy can readily be imparted to the resulting products without significantly degrading the physical properties thereof. Therefore, the halogen- and antimony-containing compounds are widely used as the primary flame retardant for housing materials for electrical appliances and office equipment formed of ABS resins, PS resins, PBT resins, PET resins or epoxy resins. However, hydrogen halide gases released by halogen-containing compounds during processing can have fatal effects on the human body and have high environmental persistence because these compounds are not naturally degradable. Also these compounds are not soluble in water, and thus can be highly bioaccumulated. Particularly, polybromodiphenyl ether, which is widely used as a halogen-containing flame retardant, may produce toxic gases such as dioxin or furan during combustion, and is consequently harmful to humans and the environment. Accordingly, there is a need to develop flame retardancy methods that do not employ halogen-containing compounds.